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Full text of "Handbook Of Chemical Engineering - I"

316
CHEMICAL ENGINEERING
COTTON: PERCENTAGE OF STRENGTH Loss
Baghouses.Woolen or cotton cloth bags of the general dimensions of 30 ft. in length and 18 in. in diameter are used. Wool is preferable to cotton because it resists heat and acids better. In a severe test by lies with roaster smoke a test cotton bag had holes in it in 20 min. A woolen bag was eaten through in 2H hoc- A-t comparatively low temperatures both cotton and wool lose strength. Alexander has tested for the loss of strength in both cloths following the subjection of test pieces to varying temperatures and different amounts of time with the following results:1
The nap which is on the cloth seems essential to the filtration process as cloth woven of material without nap lets through the fume. About 2 cu. ft. of fume per minute to the square foot of cloth surface seems to be the capacity of baghouse cloth, with 24 threads per in. in warp and woof. The bags are shaken by hand from one to eight times a day. If the bags are in bad condition owing to fume attack the slight shaking which this implies as compared with machine shaken filters tends to lengthen their life. For ordinary lead blast-furnace work cotton cloth is preferable on account of lesser cost. For corrosive fume wool should be favored and it is said that wool dyed with titanium chloride resists chemical attack well. The pressure at the bags is frequently less than 0.10 oz., more would be desirable. If the bags are well distended yet capable at the same time of being closed off entirely by pressure with the hands it is reckoned sufficient for the purpose of effecting filtration. At some of the western lead smelters bags are now shaken by machinery at
periods ranging from 15 to 30 minutes. Average data with woolen cloth filtration at these smelters is: Ib. of dust per cu. ft. of smoke, 0.00016; volume of smoke filtered per sq. ft. of bag per min. is 0.477 cu. ft. at 150F.; sq. ft. of bag per cu. ft. of smoke 2.1; temperature of smoke entering bag house 150F.; velocity in dust chambers 8.8 ft. per sec. (This is somewhat at variance with the dictum
iH. H. ALEXANDER, "The Baghouse in Lead Smelting," Trans. A. I. M. E., XLIX, p. 561.
Tempera-	Time in test oven, hours				
ture,					
degrees Fahrenheit	1	24	48	96	144
210		0.00			0.0
215		0.00	0.9	6.1	9.4
220		4.20			
225		5.25			
230		7.30			
235		12.10			
240		17.10			
245		20.70			
260	0.3				
265	3.5				
270	5.3				
280	9.6				
WOOL: PEECENTAGE OF STRENGTH Loss
270		0.0	0.0	0.0	0.0
275				0.3	3.2
280			0.0	5.3	6.9
285			0.0		
290		0.0	2.8		
295		4.0			
300		10.7			
355	0.0				
365	0.0				
370	2.3				
375	4.4				
385	6.7